There has hitherto been known an optical disc system for recording/reproducing various data by scanning a concentrically or spirally extending track on the disc by a laser beam, in which the optical disc is driven at a constant linear velocity (CLV) or at a constant angular velocity (CAV) for recording/reproducing the data. There has also been known an optical disc system of a continuous servo system in which tracking control is performed using a continuous pre-groove formed along the track, or of a sample servo system in which tracking control is performed using discrete servo areas formed on the track.
Among known types of the optical discs, there are a recordable RAM disc, such as a replay-only ROM disc, a write-once disc or a magneto-optical disc (MO disc) and a so-called partial ROM disc having both ROM and RAM areas.
An optical disc system, handling such optical disc, is configured for reading the parameter information for the medium recorded on a phase encoded part (PEP) provided on an inner rim of the optical disc as prescribed in ISO MO 5.25 inch standards and for reading the control information from the control track based upon the control information for carrying out the control operation responsive to the control information.
With the continuous composite servo system (CCS system) standardized in ISO, servo data is affected by data per se. That is, if data recording density is increased, system clocks can be reproduced with increasing difficulties, such that it becomes difficult to achieve high recording density. Besides, since the groove and pits must be cut simultaneously, it is difficult to produce a ROM disc or a partial ROM disc.
In addition, with the conventional optical disc, a dedicated decoding circuit has been required for reading out the parameter information recorded on the PEP. Since the PEP lacks in the address information, the pickup position cannot be identified. Since the PEP and the recording area for data per se are different in formats, the two areas need to be demarcated from each other via a gap.
It is therefore an object of the present invention to provide an optical disc of a sample servo system of high capacity and high performance, and a driving system therefor.
It is another object of the present invention to provide an optical disc in which the parameter information can be read without requiring a dedicated decoding circuit and in which the pickup position can be identified.